The COVID-19 pandemic has had unprecedented and deteriorating effects on the mental health of adolescents and young adults. Various studies have described changes regarding substance abuse, but findings are conflicting. We conducted across-sectional online survey on nicotine, alcohol, and illicit drug use. From March to May 2023, 502 participants aged 14-24 from acommunity-based sample completed the questionnaire. We found ageneral trend of declining or stable substance use during the first 2years of the pandemic; however, in the third year (i.e., 2022), substance use returned to pre-pandemic levels or exceeded it. Compared with young adults (age19-24), adolescents' (age14-18) use increased more clearly. Participants who scored above the cut-off on screening measures for problematic substance use showed amore pronounced increase in the use of cigarettes and illicit drugs but not of alcohol. Higher alcohol consumption during lockdowns was associated with increased likelihood of current problematic alcohol (odds ratio [OR]: 3.03) and cannabis use (OR: 2.60). Furthermore, individuals who reported increased usage of one psychotropic substance during lockdowns were more likely to have increased their use of other substances as well (OR: 2.66-4.87). Although not optimally generalizable due to the retrospective online format and convenience sampling, our results support the notion that special attention ought to be paid to certain subgroups such as younger people and those who already exhibit problematic substance use during the pandemic. Following up on post-pandemic trends in substance use is crucial for developing prevention measures and targeted interventions.